Phase margin of opamp in bandgap reference

[ipsc]

could you explain the second issue in details?
I can't understand low Vdsat can reduce the offest of opamp

Suppose there is a diffrence of 'dI' in diff-pair currents due to mismatch. This will be seen at the input as an I/P OFFSET='dI/gm'. Here 'gm' is 'gm' of diffpair. So to have low offset 'gm' should be more i.e. for a given 'Id', 'vdsat' should be low.
(Ref: Baker, Lee, Boyce).

Hope I am able to make my point clear.

Regards

 

[winsonpku]

Thanks for your warm explanation.
In fact, i think reduce the offset of opamp, biger gm of input transistor is more accurate than lower Vdsat.

could you explain the second issue in details?
I can't understand low Vdsat can reduce the offest of opamp

Suppose there is a diffrence of 'dI' in diff-pair currents due to mismatch. This will be seen at the input as an I/P OFFSET='dI/gm'. Here 'gm' is 'gm' of diffpair. So to have low offset 'gm' should be more i.e. for a given 'Id', 'vdsat' should be low.
(Ref: Baker, Lee, Boyce).

Hope I am able to make my point clear.

Regards

 

[shaq]

could you explain the second issue in details?
I can't understand low Vdsat can reduce the offest of opamp

Suppose there is a diffrence of 'dI' in diff-pair currents due to mismatch. This will be seen at the input as an I/P OFFSET='dI/gm'. Here 'gm' is 'gm' of diffpair. So to have low offset 'gm' should be more i.e. for a given 'Id', 'vdsat' should be low.
(Ref: Baker, Lee, Boyce).

Hope I am able to make my point clear.

Regards

So, I need the bigger size of diff-pair because gm must be larger, right?

 

[ipsc]

could you explain the second issue in details?
I can't understand low Vdsat can reduce the offest of opamp

Suppose there is a diffrence of 'dI' in diff-pair currents due to mismatch. This will be seen at the input as an I/P OFFSET='dI/gm'. Here 'gm' is 'gm' of diffpair. So to have low offset 'gm' should be more i.e. for a given 'Id', 'vdsat' should be low.
(Ref: Baker, Lee, Boyce).

Hope I am able to make my point clear.

Regards

So, I need the bigger size of diff-pair because gm must be larger, right?

yes, you are right!, shaq

winsonpku, I agree with you.